1. Field of the Invention
This invention is directed to Group II metal overbased sulfurized alkylphenate compositions and, in particular, to Group II metal overbased sulfurized alkylphenate compositions derived from alkylphenols enriched in substantially straight chain C.sub.12 to C.sub.22 alkyl substituents attached to the phenol ring in a "middle" position.
2. State of the Art
The operation of diesel and spark ignition internal combustion engines is typically accompanied by the formation of sludge, lacquer and resinous deposits which adhere to the moving engine parts and thereby reduce engine efficiency. In order to prevent or reduce the formation of these deposits, a wide variety of chemical additives have been developed for incorporation into lubricating oils. These additives are commonly referred to as detergents and dispersants. Dispersants have the ability to keep deposit forming materials suspended in the oil so as to retard deposit formation during engine operation. Detergents have the ability to remove preexisting deposits from the engine during engine operation.
Among the many additives which have been developed for this purpose, Group II metal overbased sulfurized alkylphenate compositions have been found to be highly effective detergent/dispersants for use in lubricating oils. Furthermore, these additives are excellent oxidation and corrosion inhibitors and, by virtue of their alkalinity reserve, have the ability to neutralize acidic combustion and oxidation products. Such acidic products form during engine operation, particularly when operated on high sulfur containing fuels, and tend to accumulate in the lubricating oil. The ability of Group II metal overbased sulfurized alkylphenate compositions to neutralize such acidic products can be directly measured by determining the total base number (TBN) of the composition. Higher TBNs reflect a greater capacity for these compositions to neutralize acids generated during engine operation.
The preparation of Group II metal overbased sulfurized alkylphenate compositions is well known in the art and is described in detail in, for example, U.S. Pat. Nos. 3,178,368; 3,367,867; and 4,744,921, each of which is incorporated herein by reference in its entirety. Typically, such Group II metal overbased sulfurized alkylphenate compositions are prepared by treating alkyphenol in a suitable diluent (e.g., a lubricating oil) with an amount of an alkaline earth metal hydroxide, oxide and/or alkoxide in excess of that necessary to neutralize the phenol and then sulfurizing the resulting product optionally in the presence of a sulfurizing catalyst. The sulfurized product is then optionally treated with carbon dioxide to provide for the Group II metal overbased sulfurized alkylphenate composition.
Such Group II metal overbased sulfurized alkylphenate compositions are additive compositions which are used to prepare a fully formulated lubricant composition suitable for use in an internal combustion engine. Typically, the additive composition is prepared as a concentrate and is then shipped to a point where it is used to prepare fully formulated lubricant compositions by combining requisite amounts of several additive compositions, including a Group II metal overbased sulfurized alkylphenate composition, to a base stock.
In order to reduce shipping costs, the Group II metal overbased sulfurized alkylphenate composition is preferably prepared to contain as little diluent as possible. Additionally, in order to achieve the maximum amount of acid neutralization possible, the Group II metal overbased sulfurized alkylphenate composition is preferably prepared to contain as high a TBN as possible. However, because of viscosity considerations, these constraints cannot be totally satisfied and a balancing of the TBN and the amount of diluent employed with the viscosity of the Group II metal overbased sulfurized alkylphenate composition is required.
Specifically, when the amount of diluent is decreased, the viscosity of the composition is increased. Likewise, at constant diluent concentrations, increasing the TBN of the Group II metal overbased sulfurized alkylphenate compositions by using incremental amounts of alkaline earth metal oxide and/or hydroxide and/or alkoxide optionally in the presence of carbon dioxide is accompanied by increases in the viscosity of the composition. When the viscosity of the composition becomes too great, the composition becomes difficult to use in formulation procedures primarily because of handling problems. When this occurs, the viscosity of the composition must be reduced and this can be accomplished either during its manufacture by reducing the amount of carbon dioxide and alkaline earth metal oxide, hydroxide or alkoxide employed or after its manufacture by adding additional diluent.
Thus, while Group II metal overbased sulfurized alkylphenate compositions produced in the prior art are reported to possess TBNs of up to about 350 or more, in practice, commercial Group II metal overbased sulfurized alkylphenate compositions typically have a TBN of less than about 300, and more typically less than about 275, so as to ensure that the composition possesses acceptable viscosity.
In view of the above, it would be particularly desirable to reduce the viscosity of Group II metal overbased sulfurized alkylphenate compositions. In particular, such reductions would mean that at constant viscosity, a higher TBN could be achieved or at constant TBN, a lower viscosity could be achieved.
In this regard, Liston, U.S. Pat. No. 4,744,921, discloses that, at constant TBN, the use of a sulfurization catalyst during synthesis of the Group II metal overbased sulfurized alkylphenate composition reduces the viscosity of the composition as compared to the viscosity of the composition prepared without a sulfurization catalyst. However, notwithstanding the reductions achieved by using such sulfurization catalysts, it would be particularly beneficial to provide for alternative methods to reduce the viscosity of the Group II metal overbased sulfurized alkylphenate compositions or to provide for any incremental reductions in the viscosity of these compositions.